Vulnerability Allowed Attackers to Join Zoom Meetings

A vulnerability in the Zoom online meeting system could allow attackers eavesdrop on meetings and view all shared content, Check Point security researchers have discovered. 

Zoom is a platform that provides video conferencing with real-time messaging and content sharing. It includes support for both desktop and mobile devices and offers end-to-end encryption for meetings and team chats.

The discovered weakness, Check Point says, was that in some cases a meeting would only be secured with the Zoom Meeting ID, which is composed of 9, 10 or 11 digits. 

Vulnerable situations, the researchers say, include those where the “Require meeting password” option wasn’t enabled, or when there was no Waiting Room enabled, for the manual admission of participants. 

What Check Point’s security researchers discovered was that an attacker could predict Meeting IDs and potentially join active meetings. 

What the researchers did was to generate multiple potentially valid Zoom Meeting IDs and prepared the URL string for joining the meetings, and then check whether the IDs were valid or not. 

A “div” element in the HTML Body of the returned response when accessing the “Join Meeting” URL was what provided information on the validity of the ID, and they also found a way to automate the verification process.

“We were able to predict ~4% of randomly generated Meeting IDs, which is a very high chance of success, comparing to the pure brute force,” Check Point explains. 

The researchers disclosed the issue to Zoom in July 2019 and in September the company made several changes to its clientinfrastructure to eliminate the vulnerability.

Zoom now requires a password when scheduling new meetings, for instant meetings, and for Personal Meeting ID (PMI). 

Furthermore, Zoom will no longer automatically indicate if a meeting ID is valid or invalid. Instead, the page loads and attempts to join the meeting, which increases the time an attacker needs to find a valid meeting. 

Additionally, repeated attempts to scan for Meeting IDs result in the device being blocked for a period of time. 

Zoom is not alone in exposing online meetings to possible eavesdropping. Late last week, Cisco warned customers that attackers had actively exploited a vulnerability (CVE-2020-3142) that allowed unauthorized users to join password-protected Webex meetings. Cisco has patched the flaw.

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